Kamloops trout (Salmo kamloops) from Kootenay lakes, obtained from eggs produced at the end of the spawning season, had fewer scales than the general run. A random sample of eggs spawned during the middle of the run were removed from the hatchery June 24, and reared at about 5[degree] C. above the water in the hatchery. In these fry the average number of scale rows was reduced by 10 from the normal average for the population. Eggs from one of the 6 pairs of fish procured at the end of the spawning season were divided into 2 lots, lot 1 being reared at ordinary temp., and lot 2, 5[degree] C. above the normal. The fishes resulting from lot 2 had the number of scale-rows still further reduced. The experiment demonstrates, not only why southern trout or those of warmer waters have fewer scales than those of colder waters, but also the variation in the same body of water, the trout from the later end of the spawning season, when the water has warmed up, having fewer scales than those hatching earlier.